Ventilation and COVID-19

Ventilation and COVID-19

Garth Hunter

Occupational Hygienist

MSc, ROH SAIOH, CM Saiosh

Content

To achieve the following understanding:

Transmission mechanisms

Types of ventilation systems

Controls / recommendations specific to COVID-19

Notes:

This presentation pulls the outstanding work of multiple people / organisations together

particularly Dr Greg Kew, REHVA, AIHA & ASHRAE

Size of Droplet / Aerosol Critical

Not only N95 & HEPA

Droplets vs Aerosols

• “Droplets traditionally have been defined as being

>5 µm in size https://www.cdc.gov/infectioncontrol/guidelines/isolation/scientific-

review.html

• CDC also say: web page, “Aerosols 101” presentation: https://t.co/HXnHGnf2up?amp=1

https://jamanetwork.com/journals/jama/fullarticle/276

3852

Speaking produces 100x more aerosol than droplets

Sneezing

COVID-19 Airborne disease

Lidia Morawska1,*,

Donald K. Milton2

239 scientists

signed commentary

Defining transmission by Exposure path

Inside the body:

RESPIRATORY VS NON-

RESPIRATORY

> 5µm URT < 5µm LRT

Outside the body:

DROPLETS, physics based cut-off 60-

100µm

Sprayed: Ballistic drops > 100µm,

direct hit on eye nostril or mouth

Droplets / Aerosol inside the body & outside the body are different

sizes – important for ventilation

Transmission: Droplets vs Aerosols

Primary transmission mechanism

of COVID-19 is through aerosol

not large droplets

Measles has R0 of 15

COVID-19 has R0 of 5.7, flu has

R0 of 1.3

COVID-19 does not spread

between floors on multi-story

buildings

Measles is a high-contagiousness aerosol-driven disease. COVID-19 is likely a

lower-contagiousness aerosol driven disease. It infects best at close proximity, also

at the room scale if we “help it along” (indoors, low ventilation, long time, no

masks). And it has trouble infecting at long range 1

Evidence vs. Modes of Transmission

Droplets Fomites Aerosols

Outdoors << Indoors X ✔ ✔✔

Similar viruses demonstrated X ✔ ✔

Animal models ? ✔ ✔

Superspreading events X X ✔✔

Supersp. Patterns similar to known aerosol diseases n/a n/a ✔

Importance of close proximity ✔ X ✔✔

Consistency of close prox. & room-level X X ✔

Physical plausibility (talking) X ✔ ✔

Physical plausibility (cough, sneeze) ✔ ✔ ✔

Impact of reduced ventilation X X ✔

SARS-CoV-2 infectivity demonstrated in real world X X ✔

SARS-CoV-2 infectivity demonstrated in lab X ✔ ✔

“Droplet” PPE works reasonably well ✔ ✔ ✔

Transmission by a/pre-symptomatics (no cough) X ✔ ✔

Infection through eyes ✔ ✔ ✔

Transmission risk models ✔ ✔ ✔

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Key:

✔: evidence

✔✔: very strong ev.

X: no evidence

X: evidence against

n/a: not applicable

S Korea – call centre

S Korea – call centre

13

S Korea – call centre

Chinese Restaurant

Chinese – Buddhist bus

Definition ventilation

Not all barriers are equal

% Risk reduction

Risk assessing meetings

Virus concentration & ventilation

20

The particles generated by

respiratory activities are small

enough to stay suspended in the

air for a long time…

…unless they are removed from

the air by ventilation (and other

processes).

Ventilation STD’s – South Africa

SANS 10400-O (2011): Buildings either naturally ventilated (4.3.1) or artificially

ventilated (4.3.2). ARTIFICIAL

2 ACPH – allows comfort & prevents body odour – doesn’t smell stuffy

12 ACPH – prevents transmission of HBA – Influenza / COVID-19

Current ASHRAE CO2 guidance

• Research shows ASHRAE guidance of 700 ppm above ambient does

not prevent measles, influenza, or rhinovirus in a school or office

• SANS 10400 Part O, EN 16798 and research all align

CatIndoor Air

Quality

CO2 above

outdoor air

(ppm)

Fresh Air Face

(L/s/person)

IDA1 High <400 >15

IDA2 Medium 400-600 10-15

IDA3 Moderate 600-1000 6-10

IDA4 Low >1000 <6

Indoor Air Quality and CO2 levels and Fresh Air Face delivery (EN 16798)

Require 15L/s per person - approximately 12 ACPH

CO2 – proxy for SARS CoV2 concentrations

• Recommended COVID-19 guidance for CO2 = <400 above ambient /

800ppm

• Practically continuous CO2 dataloggers should be set to alarm at

800ppm

Natural ventilation

Three fundamental

approaches to natural

ventilation:

• Wind-driven cross

ventilation - preferred

• Buoyancy-driven stack

ventilation, and

• Single-sided

ventilation

Air conditioning system – no ventilation

• No artificial ventilation system – only ventilation

possible is through opening windows / doors

Mid-wall split

unit – with no

fresh make up air

capability does

not provide

ventilation

Split unit air conditioner + Mechanical ventilation

• Supply outdoor air is provided to each room, is

extracted and expelled outdoor,

• Virus concentration reduced through dilution

with provided outdoor air.

Hospital Positive COVID-19 patients

Hospital evidence: no infection risk at 2 m distance,

with ventilation rates at 36 L/s per person

https://doi.org/10.1016/j.scitotenv.2020.138401 –

All-Air HVAC System

Selection of engineering controls

Assessment of all buildings

Developing “Limitations of use”

ISO 16890 Filter Group Efficiencies

Coarse < 50% of PM10

ePM10 ≥ 50% of PM10

ePM2.5 ≥ 50% of PM2.5

ePM1 ≥ 50% of PM1

ISO 16890 exposes a filter to particles from 0.3 µm all the

way up to 10 µm. This comes closer to real life conditions.

EN 1822 High efficiency air filters (EPA, HEPA and ULPA)

FILTER CLASS

INTEGRAL VALUE LOCAL VALUE

EFFICIENCY

%

PENETRATION

%

EFFICIENCY

%

PENETRATION

%

E10 ≥ 85 ≤ 15 – –

E11 ≥ 95 ≤ 5 – –

E12 ≥ 99,5 ≤ 0,5 – –

H13 ≥ 99,95 ≤ 0,05 ≥ 99,75 ≤ 0,25

H14 ≥ 99,995 ≤ 0,005 ≥ 99,975 ≤ 0,025

U15 ≥ 99,9995 ≤ 0,0005 ≥ 99,9975 ≤ 0,0025

U16 ≥ 99,99995 ≤ 0,00005 ≥ 99,99975 ≤ 0,00025

U17 ≥ 99,999995 ≤ 0,000005 ≥ 99,9999 ≤ 0,0001

Changing filters

33

Changing filters not simple:

• Increased pressure load

• > Air bypassing filters

• > maintenance

• > filter changes

Conclusion ventilation beyond COVID

• Understanding of the role of ventilation in reducing influenza infections not

new – 2011 research

• Increasing the ventilation rate from 8L/s per person to 15L/s per person, US

economy would save US$37.5bn dollars per year through reduced

absenteeism and employee performance

• World pre and post COVID-19 different, including a permanent priority

change in the control of HBA – including influenza

• Recommendation to achieve ventilation rates of 15L/s per person of outdoors

air will stand even once the COVID-19 pandemic has passed

34

No one size fits all:

• Higher atmospheric pollution > reliance on filters (CO2 becomes < useful)

• Lower atmospheric pollution > reliance on outdoor air

Conclusion: consider pollution & HBA

End

Thank you